To compare the baseline characteristics of patients with multiple system atrophy parkinsonian type (MSA-P) versus those of Parkinson's disease (PD) enrolled in the Natural History Study of the Synucleinopathies (NHSS).

The differential diagnosis between MSA-P and PD is often difficult. Better diagnostic markers are required to improve diagnostic accuracy.

Patients with probable/possible MSA-P or PD were enrolled in the NHSS, a global multicenter prospective study. Detailed clinical neurological, sleep and autonomic parameters were assessed at baseline.

We included 169 patients with MSA-P and 87 with PD. PD patients were more frequently males (70% vs. 57%; p=0.13), older at entry and at disease onset (61±11 vs. 57±11; p<0.01), and had longer disease duration (8±5 vs. 5.6±5.1; p=0.01). MSA-P patients had higher UMSARS, worse quality of life, and higher burden of autonomic symptoms. PD patients had worse MoCA scores (25±4 vs. 26±5; p<0.01) and reduced olfaction (18±8 vs 28±9; p<0.01).  Urinary retention ( 77% vs. 44% p<0.001), incontinence (85% vs. 51% p<0.001) and use of indwelling catheter ( 51% vs. 4% p<0.001) were more frequent in MSA-P patients. The frequency of orthostatic hypotension (30/15 criteria, 63% vs. 58%) and supine hypertension (55% vs. 51%) was similar. MSA-P patients had a faster resting heart rate (75±11 vs. 68±11 bpm p<0.001). A composite score comprising heart rate > 67 bmp, UPSIT > 26, and urinary incontinence had a 76% sensitivity and 91% specificity to distinguish MSA-P from PD.

Age at onset of MSA-P was 5 years younger than that of PD. Despite shorter disease duration at enrollment, MSA-P patients had higher symptomatic burden. The severity and prevalence of orthostatic hypotension and supine hypertension, however, were similar in MSA-P and PD. Taken together, urinary incontinence, preserved olfaction, and a higher resting heart rate can help distinguish MSA-P from PD.